1. Technical Field
This invention relates generally to rechargeable batteries having associated memory circuits, and more particularly to rechargeable battery circuits having a multiplexed, three terminal memory.
2. Background Art
Electronic memory devices have been around for many decades now. They come in many forms. One very popular type of memory is the electrically programmable read-only memory (EPROM). This device is a non-volatile, transistor based memory that is electrically programmable. The “non-volatile” feature means that an EPROM will retain data even after its power source has been removed. While older memory devices were programmed by physically blowing specific transistors, an EPROM is capable of being programmed electronically. Typically a microprocessor “writes” to the device to program, or store data in, the device.
EPROM devices, generally speaking, are known in the art. For example, U.S. Pat. Nos. 5,483,094, 5,498,560, 5,543,339, 5,554,869, 5,616,941, and 5,621,233, all assigned to Motorola, Inc., teach how to make and use the silicon die and circuitry used with such devices. These patents are incorporated herein by reference.
Another popular memory device is the electrically erasable, programmable, read-only memory (EEPROM). This type of memory is a transistor based, overwritable, non-volatile memory. The “overwritable” feature means that the information stored in the EEPROM may be erased and overwritten. EEPROMS use very similar circuitry to EPROMS. They simply have the added feature of being electrically eraseable. EEPROM devices, generally speaking, are known in the art. For example, U.S. Pat. Nos. 4,479,203, 5,034,922, and 6,438,030, all assigned to Motorola, Inc., teach how to make and use the silicon die and circuitry used with such devices. These patents are incorporated herein by reference. (While the discussion herein after will refer to EPROMs, it will be understood by those of ordinary skill in the art that EEPROMs may be substituted for EPROMs when the writable functionality is required.)
Traditionally, EPROM devices included more than 4 pins. There was a plurality of data pins, as well as power, ground and a clock pin. Dallas Semiconductor greatly simplified the structure of EPROM by developing their “one-wire interface”. The one-wire interface is a two pin EPROM. One pin is used for power and data. The other pin is used as ground. One example of such a device is the DS2502 one-wire EPROM. The data sheet for this part may be found by way of the Internet at the address: http://dbserv.maxim-ic.com/quick view2.cfm.?qv pk=2924. (An example of an EEPROM is DS2433 4 k-bit one-wire EPROM. http://dbserv.maxim-ic.com/quick view2.cfm.?qv pk=2915.) The one wire structure is taught in several patents assigned to Dallas Semiconductor, including U.S. Pat. Nos. 5,210,846, 5,398,326, 5,809,518, 5,864,872, and 6,108,751. These data sheets and patents are incorporated herein by reference.
Many creative applications have been developed for EPROM devices like the DS2502. For example, U.S. Pat. No. 6,054,843, entitled “High Speed Battery Charging System with High Accuracy Voltage Sensing,” assigned to Motorola, teaches a rechargeable battery pack having such a device. This patent is incorporated herein by reference. While this application works well, there is constant pressure on designers of such battery packs to reduce costs. It would thus be advantageous to have an improved battery circuit with memory with a lower cost.